Chapter 2: Enzymes Flashcards Preview

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Flashcards in Chapter 2: Enzymes Deck (45):
1

Isomerase

type of enzyme that converts a compound to its isomer by rearranging its bonds

 

A ⇒ B (Isomer of A)

 

2

What are the 6 enzyme categories?

And what do each of them do?

Remember: LIL HOT

Ligase - use ATP to catalyze addition/synthesis rxns

Isomerase - converts a compound into its isomer by rearranging bonds

Lyase - breaks down bonds by forming double bonds or rings; without using water

Hydrolase - breaks down bonds using water

Oxidoreductase - catalyze redox rxns by transferring electrons between molecules

Transferase - transfers functional groups from one molecule to another

3

Cofactors

metal ions that bind to enzyme active sites and participate in catalyzing reactions.

inorganic

We get our cofactors from minerals.

4

active site

catalysis site on an enzyme where substrates bind to during reactions 

5

irreversible inhibition.

What is the only way to increase reaction rate?

What does the inhibitor do to the enzyme?

  • Occurs when an inhibitor deactivates an enzyme for a prolonged period of time or permanently.
  • Removing the inhibitor from the enzyme does not reactivate the enzyme.
  • The inhibitor binds covalently to the active site of the enzyme, which is a very strong/permanent bond

__________________________________________

To increase reaction rate, add more enzymes

6

What process controls enzyme activity?

Feedback regulation controls enzyme activity. 

Feedback regulation occurs when products of a reaction affect enzyme activity.

7

at High Km:

Is the Substrate concentration low or high?

Is the enzyme's affinity (want) for substrates low or high?

At High Km:

Substrate concentration at half max velocity is HIGH

Enzyme affinity for more substrates is LOW, because there are already so many substrates 

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8

what are the fat soluble vitamins?

 

 

water soluble vitamins?

 

what do they do?

Fat soluble: ADEK

Vitamins A, D, E, K

 

 

Water soluble: the others

B, C

 

They are coenzymes, that help enzymes function

9

negative feedback on enzymes

As more products are produced, they competitively inhibit the active sites of enzymes which blocks substrates from binding.

 

This prevents more products from being made, since there already are enough. 

10

What is Km (Michaelis Menten Constant)

Km is the substrate concentration when the reaction is at half max velocity.

 

Km: [S] at ½Vmax

11

Exergonic reaction.

Is it a spontaneous or nonspontaneous reaction?

reaction where the system loses energy

Reactants have more energy than Products.

 

█ ⇒ ▂

 

It is spontaneous (ΔG is negative), because it already contains the energy needed for it to occur

 

12

at Low Km:

Is the Substrate concentration low or high?

Is the enzyme's affinity (want) for substrates low or high?

At low Km:

Substrate concentration at half max velocity is LOW

Enzyme affinity for more substrates is HIGH, because it wants more substrates to reach max velocity

 

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13

inhibition types and their effect on Km and Vmax

 

Competitive

Noncompetitive

Mixed

Uncompetitive

If the enzyme does not have the substrate: they don't love each other; Km is high and affinity is low

If the enzyme has the substrate: they love each other; Km is low and affinity is high

  • competitive inhibition - substrate and inhibitor try to bind to the active site
  • noncompetitive inhibition - inhibitors bind to the allosteric site of either the E-S complex or enzyme alone
    • Type of mixed inhibition
  • mixed inhibition - inhibitors bind to the allosteric site of either the E-S complex or enzyme alone
  • uncompetitive inhibition - inhibitor bind to the allosteric site only on the E-S complex

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14

What is the enzyme-substrate complex?

the substrated and enzyme bound together

15

Ligase

type of enzyme that uses ATP to catalyze addition and synthesis reactions.

 

A+B ⇒ AB

Example: DNA Ligase adds two pieces of DNA together during DNA replication

16

Enzymes

Do enzymes affect the thermodynamics of a reaction?

 

Proteins that speed up reactions by lower activation energy.

Enzymes are not consumed in the reaction.

(appear in both reactants and products)

________________________________________

Enzymes affect reaction kinetics speed but not thermodynamics.

Enthalpy (ΔH) , Equilibrium positon, and Free energy (ΔG) are the same with/without enzymes 

17

Oxidoreductases

What are oxidoreductases named?

type of enzyme involved in redox reactions, the transfer of electrons from one molecule to another.

 

A: + B ⇒ A + B:

 

________________________________________

Many have the following in their names:

Dehydrogenase, Reductase, and Oxidase 

18

transferase

type of enzyme that transfers functional groups from one molecule to another.

 

AX + B ⇒ A + BX

(Transfers functional group "X" from molecule A to B)

19

What is Reversible Inhibition of Enzymes?

What are the 4 types of reversible inhibition and their definitions?

Reversible inhibition occurs when an inhibitor deactivates an enzyme. The inhibitor can leave, restoring the enzyme function.

_________________________________________

  • Competitive inhibition - an inhibitor binds to the active site of an enzyme, blocking the substrate
  • Noncompetitive inhibition - an inhibitor binds to an allosteric site of either an E-S complex or enzyme alone
    • They don't affect the enzyme's affinity for substrate; thus, Km remains the same
  • Mixed inhibition - an inhibitor has an unequal affinity to bind to the allosteric site of either an E-S complex or enzyme alone
    • If it binds to the E-S complex; the substrate is already in the enzyme; thus Km decreases because affinity for S increases

    • If it binds to the enzyme alone; the substrate is not in the enzyme; thus Km increases because affinity for S decreases

  • Uncompetitive inhibition - an inhibitor binds to an allosteric site of an E-S complex, locking the substrate in so the rxn cannot complete
    • It binds to the E-S complex only; thus Km decreases because affinity for S increases

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20

Enzyme/Substrate Interaction Theories:

(1) Lock and Key theory 

(2) Induced Fit Theory

__________________________________________

Define each. Which one is most accepted?

(1) Lock and Key theory - a substrate has a specific shape that fits perfectly into an enzyme's active site.

 

(2) Induced Fit theory - a substrate interacts with the active site of an enzyme, until they both fit perfectly together.

[Induced Fit is most accepted.]

21

Uncompetitive inhibition

How is Vmax and Km affected by this inhibition?

Occurs when inhibitors bind to the enzyme-substrate complex and lock the substrate in, preventing the reaction from completing.

__________________________________________

Both Vmax and Km decrease.

There becomes a smaller amount of active enzymes, so both decrease.

22

What happens to the rate of the reaction as more substrate is added to enzymes?

  • At first, adding more substrate leads to a proportional increase in the rate of the reaction.
  • Once most of the active sites are occupied, the reaction rate levels off regardless of further substrate additions.
  • At high substrate concentrations, all active sites become occupied and the maximum velocity is reached.
    • Adding more substrate does not increase the reaction rate

 

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23

hydrolase

type of enzyme that uses water to breakdown a single molecule into two products.

 

A + H2O ⇒ B + C

24

At what temperature do most enzymes work best in the body?

Enzymes work best at 98.6°F (37°C or 310K)

 

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25

What happens to an enzyme when substrate concentration reaches saturation.

Saturation occurs when the reaction cannot go any faster. The rxn is at Max Velocity.

At saturation, the enzymes are holding the maximum amount of substrates that they can handle

__________________________________________

To inrease the max velocity of the reaction, enzyme concentration must be increased

26

Kinase

part of the transferase enzyme class.

Kinase transfers phosphate functional groups between molecules

27

What is the michaelis menten equation?

What are the relationships between variables?

Reaction Velocity = (Max Velocity · [S]) / (Km + [S])

________________________________________

[S] is substrate concentration.

Km is the [S] at half the rxn's max velocity

________________________________________Reaction velocity increases as the max velocity and substrate concentration increases. (Vmax + [S])

Reaction velocity decreases as more enzymes are required to fill all enzyme active sites. (Km + [S])

28

Lyase.

What are lyases named?

Type of enzyme that breaks a single molecule into two by forming a double bond or ring.

Lyases do not use water or electron transfer (redox).

They do not use water to catalyze the reaction.

They can also turn 2 molecules into one.

A ⇒ B + C

________________________________________Many have "Synthase" in their names

 

 

29

At what pH do most enzymes work best in the body?

What are the exceptions and where are the enzymes?

Most enzymes work best at pH 7.4 in the human body.

__________________________________________

Exceptions:

pH 2 is best for enzymes in the digestive system.

pH 8.5 is best for enzymes in the pancreas 

30

How do enzymes speed up reaction?

They lower the activation energy without being lost in the reaction. This makes it easier for substrates to reach their transition state.

__________________________________________

They do not affect the enthalpy, free energy change (ΔG ), or equilibrium position of the reaction

 

31

Allosteric Enzymes.

Allosteric Activators

Allosteric Inhibitors

Enzymes that contain an active site and atleast one allosteric site.

Binding at the allosteric site causes the enzyme to undergo conformational change. 

________________________________________

  • Allosteric activators make the active site more available for substrate binding.
  • Allosteric inhibitors make the active site less available for substrate binding

32

enzymes and equilibriums

what can enzymes do to equilibriums?

enzymes do not affect equilibriums themselves

 

but they can increase the rate at which equilibrium is reached

33

Noncompetitive inhibition

How is competitive inhibition overcome?

How is Vmax and Km affected by this inhibition?

Occurs when inhibitors bind to the allosteric site of an enzyme, which changes the active site's conformation and prevents substrates from binding.

________________________________________

Increasing enzyme concentration can overcome the inhibition.

________________________________________Max velocity decreaes since enzymes become deactivated (Vmax decreases).

Km remains constant because there is a fixed amount of inactive enzymes and only active enzymes determine Km. 

 

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34

Zymogens

Inactive enzymes that only become active once they are needed by removing their regulatory structure. 

They may be dangerous if not controlled.

__________________________________________

They contain a regulatory structure that keeps them inactive.

 

35

Competitive inhibition.

How is competitive inhibition overcome?

How is Vmax and Km affected by this inhibition?

inhibitors occupy the active site, preventing a substrate from binding to it. 

________________________________________

To overcome competitive inhibition, increase substrate concentration.

So there are way more substrates than inhibitors to compete for the active site

________________________________________The max velocity is the same. (Vmax is constant).

Km increases because more substrates are needed to reach max velocity. (Km increases).

 

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36

endergonic reaction.

Is it a spontaneous or nonspontaneous reaction?

reaction where the system gains energy.

Products have more energy than reactants.

▂ ⇒ █ 

 

It is nonspontaneous (ΔG is positive), because it requires energy to occur

37

Cooperative enzymes

multiple active site enzymes which undergo substrate affinity changes depending on whether substrates bind or leave the active sites.

________________________________________

As more substrates bind to the enzyme, the enzyme progressively becomes more attracted to substrates.

________________________________________

As more substrates leave the enzyme, the enzyme progressively becomes more likely to remove its substrates

38

Apoenzymes

inactive enzymes because they lack their cofactors or coenzymes

39

Mixed inhibition

How is Vmax and Km affected by this inhibition?

occurs when an inhibitor has an unequal affinity to bind to the enzyme-substrate complex or the enzyme alone. 

  • Inhibitor knocks out substrate when it binds to enzyme-sub complex.
  • Inhibitor blocks substrate when it binds to the enzyme alone

________________________________________

  • Km increases if the inhibitor prefers the enzyme alone.
  • Km decreases if the inhibitor prefers the enzyme-substrate complex
  • Max Velocity decreases in both conditions.

 

40

can Km be altered by changing the concentration of substrate or enzyme?

no

 

Km is an innate property of the enzyme-substrate system

 

41

How does the plot of Cooperative Enzymes look on a Rate of Reaction vs Substrate Concentration graph?

(Draw it out)

The plot is sigmoidal (S-shaped).

Initially, more [S] slowly increases reaction rate.

As more substrates are added, the reaction rate gets progessively faster and faster.

Until all of the active sites are occupied and the max reaction rate is reached.

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42

Coenzymes

small organic molecules that bind to enzyme active sites and participate in catalyzing reactions.

 

We get our coenzymes from vitamins. 

43

Holoenzymes

active enzymes with their cofactors and coenzymes.

44

Enzyme Kinetics question

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Once the enzyme is saturated with the substrates it needs to do the reaction, it doesn't matter what the substrate concentration is outside of the enzyme

 

C

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45

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